Rotor construction for induction-motors.



J. D. NIES.

ROTOR CONSTRUCTION FOR INDUCTION MOTORS.

- APPLICATION FILED FEBJS, 1912. 1,092,849.

Patented Apr. 14, 191i UNITED STATES PATENT OFFTSE.

JOHN D. NIES, OF ST. CHARLES, ILLINOIS, ASSIGNOR TO KIMBLE ELECTRIC CO., OF CHICAGO, ILLINOIS.

ROTOR CONSTRUCTION FOR INDUCTION-MOTORS.

To all 2071 am it may concern Be it known that I, JOHN D. Nlns, a citizen of the United States of America, and a resident of St. Charles, county ,of Kane, State of Illinois, have invented certain new and useful Improvements in Rotor Construction for Induction-Motors, of which the following is a specification.

The main objects of this invention are to provide in an induction motor an improved rotor having improved means for automatically changing the resistance of the windings of said rotor during the process of starting; to provide an improved rotor which will start and accelerate up, to any predetermined speed before taking up the load with out requiring any outside controller or compensator; to provide an improved rotor which at its normal running speed will operate with high torque and efiicient current consumption; to provide improved means for changing the mechanical arrangement of the rotor windings during acceleration in such manner as to obtain free rotation of the rotor at starting and a high torque at comparatively high speed with an efficient current consumption both in starting and at full speed, and to provide an improved squirrel cage winding which will eliminate the usual wire winding and its resulting bulky, costly construction, low power factor, lowefliciency, low overload capacity and low pull out torque.

Heretofore the change of resistance in the rotor has usually been accomplished by the use of a wire winding, sometimes in the form of a so called phase winding, provided with slip rings through which a resistance is inserted for starting conditions and cut out for full speed conditions; and sometimes as a winding connected to a commutator with means for short circuiting the commutator on full speed running, the wire winding being necessary in order to secure higher voltage and lower current than is employed in the conductors of the usual squirrel cage winding, in order to avoid trouble through the contact deteriorating through wear or dirt, which trouble would be very serious wit-h the low voltage and heavy current employed in squirrel cage windings. In a squirrel cage the current may be in the order of 1000 amperes at a potential of less than Specification of Letters Patent.

Application filed February 1 5, 1912.

full speed of the motor.

Patented Apr. 1%, rare.

Serial No. 677,757.

one volt, hence permanently clean contacts are essential.

A specific construction illustrating this invention is shown in the accompanying drawings, in which- Figure 1 is a partly sectional side view of a rotor adapted to automatically change its resistance with change of speed. Fig. 2 is a transverse section of the same taken on the line AA of Fig. 1, showing both the high resistance and the low resistance windings. Fig. 3 is a fragmentary longitudinal section taken on the line BB of Fig. 2.

In the construction shown in the drawings the rotor comprises a drivin member or magnetic element 1 and a driven member or shaft 2 journaled to rotate relatively to each other about the same axis, and adapted to be operatable in any induction motor field, the driving member 1 being loosely carried by the shaft 9., and comprising the usual thin metal stampings or disks 8 which are clamped together and mounted on the quill shaft 5 which is normally free to rotate upon the main shaft 2. An annular series of openings or slots 4 extend through said driving member from end to end and are spaced apart circumferentially.

The driven member comprises the main shaft 2 and a pair of end plates 6, preferably of low resistance metal, such for example as copper. The end plates 6 are fixed to the shaft and also serve to limit the axial movement of the quill shaft 5 on the main shaft 2. An annular series of perforations, each containing a conductor bar 7 of comparatively high resistance, is located adjacent to and between the slots 4. The bars 7,

which are riveted to the end rings 7, act as a high resistance winding and also serve to fasten the disks 3 together. The slotted openings 4 are provided with bars 8 of low resistance, which project outwardly from the driving member at each end thereof. The outer face of each of the projecting ends of said bars serves both as a clutch face and as an electrical contact surface. The bars are normally held at the inner side or bottom of the slots by springs 9 which are so proportioned that they will yield and permit the bars 8 to be moved out by centrifugal force at substantially one half the normal The end plates 6 are provided with inwardly facing annular shoulders or flanges providing surfaces 10 serving as clutch faces and also as electrical contact surfaces coacting with those of the low resistance bars 8 when the latter are shifted outwardly by centrifugal force.

The operation of the device is as follows Beginning with the rotor at rest when the stator is excited, the low resistance conductor bars are normally held out of circuit by the springs- 9 and the magnetic por tion of the rotor is rotatable on the motor shaft 2 independent of the rotation of the shaft 2, because the quill shaft 5 is loose upon the shaft 2. The high resistance bars will be acted upon and the motor will be quick in starting and will take low current because of the rotors comparatively high resistance winding, and because of the absence of load. As the rotor accelerates the torque efliciency will begin to diminish. At a predetermined point or speed the low resistance bars will be thrown outward and into contact with the low resistance end plates 6. At first the outward pressure of the bars against the end plates will be slight and there will be a momentary slippage or rubbing between the bars and the end plates which serves to keep the contact surfaces permanently clean, bright and of low re sistance. The conducting bars 8 become not only low resistance windings for the rotor but at the same time mechanically hold the magnetic portion of the rotor to the end plates and thereby transmit the energy of rotation from the magnetic rotor to the end plates which are fastened to the motor shaft 2, thereby starting the load. As the motor passes the predetermined speed the shifting of the low resistance windings to make contact with the end plates alters the torque characteristic of the rotor so that the rotor will now have its maximum torque at approximately full load speed. As is well known when it is necessary in polyphase motors with low resistance rotors to start the load, it is the common practice to provide means by which approximately four times the normal full load running current is used to start the motor, and that high resistance rotors have not been considered practical because of the rapid fall in torque and the low resistance rotor, the combination of the high resistance rotor and the low resistance rotor as here set forth will maintain a high torque under practically all operating conditions and will be capable of starting substantially at full load from rest without the use of extra controllers or compensators.

Although but one form of this rotor is here illustrated in the drawings, it will be understood that numerous details of the construction shown may be altered or omitted without departing from the spirit of the invention as defined by the following claims:

I claim 1. In a rotor adapted to be used in an induction motor field, the combination of a driving member and a driven member journaled to rotate relatively to each other, said rotor having a normally closed high resistance winding and a normally open low resistance winding, said low resistance winding comprising a portion of said driven member and means rotatable with said driving member and adapted to be shifted into engagement with said driven member for mechanically and electrically connecting said members.

2. In a rotor adapted to be used in an induction motor field, the combination of a driving member and a driven member journaled to rotate relatively to each other, said rotor having a normally closed high resistance winding and a normally open low resistance winding, said low resistance winding comprising a portion of said driven member and means rotatable with said driving member and adapted to be shifted by centrifugal force into engagement with said driven member for mechanically and electrically connect-ing said members at a pre-.

determined speed.

3. In a rotor adapted to be used in an induction motor field, a fixed high resistance winding, movable low resistance bars, adapted to be shifted through centrifugal force, and means rotatably mounted coaxially with the main body of said rotor and normally disconnected therefrom when said motor is at rest or running at low speed, said means being formed and arranged to coact with said low resistance bars for the purpose of forming a low resistance winding on said rotor at a predetermined speed.

4. An induction motor comprising a. magnetic element, a high resistance winding on said element, low resistance bars movably mounted on said element and adapted to be shifted by centrifugal force, a driving shaft rotatable relatively to said element, end plates fixed on said shaft and adapted to coact with said low resistance bars for forming a low resistance winding for said rotor.

5. A rotor adapted for use with an inducile tion motor field and wound in part with fixed conductors having high resistance, conductor bars having comparatively low resistance slidably mounted on said rotor and adapted to shift through centrifugal force and means located to coact with said bars, to operate as a mechanical clutch and also as a low resistance circuit closing device at a predetermined speed.

6. In a rotor adapted to be used as an induction motor field, the combination of a driving member and a driven member journaled to rotate relatively to each other about the same axis, said rotor having a high resistance winding and a low resistance winding, said low resistance winding being normally open circuited and comprising parts carried respectively by said driving and driven elements and adapted to become engaged through centrifugal force to close the low resistance circuit and simultaneously connect said driving and driven members in driving relation to each other.

7. In a rotor adapted to be used in an induction motor field, the combination of a driven member, a driving member having a high resistance winding, a low resistance winding, said driving member having an annular series of slots adjacent to the periphery thereof and extending from end to end of said driving member, said low resistance winding comprising an annular se ries of bars slidably mounted in said slots and a pair of end plates mounted on said driven member having annular clutch faces opposed to said bars, each of said bars having clutch faces adapted to engage said annular clutch faces when said bars are shifted bycentrifugal force, and thereby mechanically connect said driving and driven members and simultaneously close the circuit of said low resistance winding.

8. In a rotor adapted to be used in an induction motor field, the combination of a driving member and a driven member adapted to rotate relatively to each other and being mounted in substantially coaxial relation, said driving member having a. high resist auce winding, and means mounted on said driving member and adapted to be shifted toward and into engagement with a suitably formed portion of said driven member during the rotation of said driving member for mechanically and electrically connecting said driving member and said driven memher, said means and said driven member being adapted when in engaged position to form a low resistance winding for said rotor.

9. In a rotor adapted to be used in an induction motor field, the combination of a driving member and a driven member adapted to rotate relatively to each other and being mounted in substantially coaxial relation, said driving member having a high resistance winding, means mounted on said driving member and adapted to be shifted toward and into engagement with a suitably formed portion of said driven member during the rotation of said driving memher for mechanically and electrically connecting said driving member and said driven member, said means and said driven member being adapted when in engaged position to form a low resistance winding for said rotor, and means normally retracting said first named means from said driven member.

10. In a rotor adapted to be used in an induction motor field, high resistance and low resistance windings, said low resistance winding comprising an annular series of bars and a pair of end plates, said end plates being mounted coaxially with said series of bars but independently thereof when the ro tor is at rest or running at a low speed, and said bars being adapted to be shifted toward and into engagement with and away from, and out of engagement with suitably formed portions of said end plates during the rotation of said rotor, for the purpose specified. 11. A rotor for dynamo electric machines, comprising a driving member having an annular series of longitudinal slots adjacent the periphery thereof, a driven member, suitably formed and normally disengaged with respect to the driving member when the rotor is at rest and an annular series of bars lying normally against the centrally facing bottoms of said slots during rest and movable radially outwardly within said slots by centrifugal force when the rotor ro tates at a predetermined speed, said bars having portions thereof extending outwardly therefrom at each end of said driving member, said extending portions being adapted for mechanically connecting said driving and said driven members when said bars are moved to their outward position.

12. A rotor for electrical induction transforming machines, comprising a driving member and a driven member journaled torotate relatively to each other about the same axis; a fixed high resistance winding and a low resistance winding, said driven member comprising a pair of end plates having inwardly disposed clutch faces and electrical contact surfaces, said driving member being mounted between said end plates and having a series of longitudinally disposed bars movably mounted thereon and spaced apart circumferentially, each of said bars having a portion extending endwise outwardly from said driving member and having clutch and electrical contact surfaces, said bars being adapted to be moved radially outward when said driving member is rotated for electrically and mechani cally connecting said driving and said driven members at a predetermined speed, said bars and said driven members being adapted to form a low resistance Winding said clutch member at a predetermined 10 for said rotor when so connected. speed.

13. A rotor comprising a shaft, a core Signed at Chicago this 10th day of Feb- :Ereely rotatable on said shaft, a clutch memruary, 1912.

her fixed upon said shaft adjacent to said core, and a Winding on said core including as an element thereof a clutch member operatable by centrifugal force to close the circuit of said Winding and to engage the first JOHN D. NIES.

Witnesses EUGENE A. RUMMLER, EDWIN PHELPS.

Copies of this patent may be obtained for five cents each, by addressing the Commissioner of Patents, Washington, D. G. 

